Calutron ion source with magnetic field inducing coil within arc chamber



3,432,709 ING E v mm illm! m m 1,4 I E kwgmgw wv E A E N I mm T mw March 11, 1969 CALUTRON ION SOURCE WITH MAGNETIC FIELD INDUC INVENTORS. John V. Lee Leon 0. Love ATTORNEY.

United States Patent 3,432,709 CALUTRON ION SOURCE WITH MAGNETIC FIELD INDUCING COIL WITHIN ARC CHAMBER John V. Lee and Leon 0. Love, Oak Ridge, Tenn., as-

signors to the United States of America as represented by the United States Atomic Energy Commission Filed Oct. 23, 1965, Ser. No. 504,274

US. Cl. 313-63 Int. Cl. Hh 11/00; Htllj 1/50 3 Claims ABSTRACT OF THE DISCLOSURE The invention described herein was made in the course of, or under, a contract with the US. Atomic Energy Commission. It relates generally to ion-producing mechanisms and more particularly to an improved ion source for electromagnetic isotope separating machines which are commonly known as calutrons.

The isotopes of many chemical elements can be separated in an electromagnetic mass spectrometer known as the calutron, described in US. Patent No. 2,709,222, by E. 0. Lawrence. In the calutron, as described in the Lawrence patent, there is provided an ion-producing means wherein a feed or charge of material containing the desired isotope is converted into ions for subsequent acceleration through a magnetic field where isotopes of different masses travel in different arcs terminating in receiverslots. Since many charge materials are solids, the charge must first be heated in a vaporizer or oven to produce a charge vapor. Vapor from the vaporizer or oven passes to an arc chamber where a stream of electrons (commonly called the arc discharge) is passed through the vapor, ionizing it for subsequent acceleration through a magnetic field. One means for heating the charge material for use in an ion source is disclosed in US. Patent No. 3,115,575 to W. A. Bell et al.

The utilization of feed materials by ion sources has long been recognized as an ineflicient process. Low utilization factors (-25%) result when most of the charge material which is vaporized is lost within the calutron where it either deposits on various surfaces or is removed by the diffusion pumps. The loss of material is highly disadvantageous in that it requires additional charge materials to be prepared and vaporized in order that a given quantity of a specific isotope may be separated. In addition, costly recovery procedures must be used to recover the charge material which is not collected in the receiver. This is especially true where the charge material is very valuble (uranium), hazardous (plutonium), or requires a second pass through the calutron to reach the desired purity.

A related problem in determining the overall efliciency of the calutron is that of ion beam oscillation which causes cross contamination of isotopic species at the calutron receiver. This problem is especially evident where the mass differences of heavy species is very small and little separation exists'between adjacent beams. In such a case, the receiver slots are very close together and only a slight oscillation in the ion beam is necessary to cause some ions to strike the wrong receiver slots. The isotopic purity of the resulting product is reduced accordingly, and in some cases where very high purity is required, the product may have to be recycled through the calutron. Such recycling is undesirable because the overall feed material utilization is reduced even further and the time required to recover the product is increased substantially due to the very low rate of product separation in a calutron.

One of the predominant causes of ion beam instabilities or oscillations has been determined to be ion oscillations at the ion source. Thus, there exists a need for some means for substantially reducing these oscillations while providing for more efficient utilization of feed material.

It is, accordingly, a general object of the invention to provide an ion source characterized by an increased efliciency in the utilization of feed material.

Another object of the invention is to provide an ion source wherein the objectionable oscillations occurring therein are minimized.

Other objects of the invention will become apparent from an examination of the following detailed description of one embodiment of the invention and the appended drawings, wherein:

FIG. 1 is a perspective view of an ion source made in accordance with the present invention.

FIG. 2 is a transverse sectional view of the ion source of FIG. 1.

In accordance with the present invention, the above objects have been achieved by the use of an electrically biased current loop within the arc chamber of an ion source. Current is caused to flow in' this loop parallel to, and above and below the arc discharge in a direction so as to create a magnetic field directed toward the ion exit slit of the ion source.

In order to facilitate an understanding of the invention, reference is first made to FIG. 1 wherein an ion source constructed in accordance with the present invention is illustrated. The conventional accelerating electrodes and ion exit slit member are not shown in order to more clear- 1y illustrate the remaining structure within the arc chamber member 1. A conventional cathode or filament 2 and shield 3 are spaced at one end of the arc chamber with first and second defining slot members 4 and 5 which define an arc column or discharge of flowing electrons. At the other end of the arc chamber, an electron reflector 6 is supported from the back of the arc chamber. A movable baffle 7 described in detail in copending application Ser. No. 470,651, now Patent No. 3,382,359, of common assignee, is disposed behind the arc column. Mounted within the arc chamber are copper current carrying conductors forming a current coil or loop 8 having an upper leg 9 above the arc discharge and a lower leg 10* below the arc discharge. A cross leg 11 between the upper and lower legs of the current coil is set behind the arc column or discharge near the defining slot member 5. Cross leg 11 need not be disposed immediately behind the arc column but may communicate in a remote manner so that current flow therethrough does not influence the desired magnetic field. Alternatively, separate current supplies may be furnished for the upper and lower legs 9 and 10 thus eliminating cross leg 11 altogether. Current and coolant water is supplied to current coil 8 through leads 12 at the anticathode end of the chamber and flows in the direction indicated by the arrows.

A current flow of from about to 400 amperes through current coil 8 has been found adequate for coil operation according to the invention. Coolant water flows through copper current coil 8 to prevent its melting although solid heat resistant and low emitting material such as molybdenum could be used without cooling as an alternative. Current coil 8 may also have a circular or annular 3 cross section, although a hollow rectangular cross section is illustrated.

Referring now to FIG. 2, a cross section view of the arc chamber 1 is shown with an ion exit member 13 in place across the front thereof. Ion exit member 13 is provided with an ion exit slit '14 adjacent to are discharge or column 15. Are column 15 has the same cross section as the slots in defining slot members 4 and 5. A movable baflie 7, as described in an earlier reference to FIG. 1, is shown behind the arc column. Shown above and below are column 15 are the upper and lower legs 9 and 10 respectively of current coil 8. In this view the main magnetic field of the calutron is normal to the section of FIG. 2; and the directions of the magnetic fields H induced by the current flow through current coil 8 are shown by the curved arrows about the legs of the current coil.

Ion sources constructed in accordance with the present invention have demonstrated an ability to provide ion outputs equal to or greater than prior art systems with a charge material feed rate which is only about fifty percent as large. The isotopic purity of the separated product has also been increased due to reduced ion beam oscillations associated with lower charge material feed rates which this invention allows without reducing the beam current. This combination of factors substantially increases the utilization of feed materials in the calutron While improving the quality of the separated product.

The above description of the invention was olfered for illustrative purposes only, and should not be interpreted in a limiting sense. It is intended rather that the invention be limited only by the claims appended hereto.

Having thus described our invention, we claim:

1. In an ion source for a calutron comprising an arc chamber, means for maintaining an arc discharge in said arc chamber, an ion exit member forming one wall of said are chamber, said ion exit member being provided with an ion exit slit adjacent to said are discharge, means for feeding vaporized material into said are discharge to provide ions, and means for extracting and accelerating said ions from said are chamber; the improvement com prising current carrying conductors mounted within said are chamber adjacent to said are discharge, said current carrying conductors providing a magnetic field upon the passage of a DO. electric current therethrough for promoting the migration of the ions formed in said are discharge through said exit slit, thereby effecting a substantial increase in the operating efficiency of said source at about one half the normal vapor feed rate.

2. In an ion source for a calutron comprising an arc chamber, means for maintaining an arc discharge in said are chamber, an ion exit member forming one wall of said are chamber, said ion exit member being provided with an ion exit slit adjacent to said are discharge, means for feeding vaporized charge material into said are discharge to provide ions, and means for extracting and accelerating said ions from said arc chamber; the improvement comprising a first elongated current carrying conductor extending parallel to and above said are discharge within said arc chamber, a second current carrying conductor extending parallel to and below said are discharge within said are chamber, said first and second current carrying conductors providing a magnetic field upon the passage of electric DC. current therethrough for promoting the migration of the ions formed in said are discharge through said exit slit, thereby effecting a substantial increase in the operating efiiciency of said source at about one half the normal vapor feed rate.

3. In an ion source for a calutron comprising an arc chamber, means for maintaining an arc discharge in said are chamber, an ion exit member forming one wall of said are chamber, said ion exit member being provided with an ion exit slit adjacent to said are discharge, means for feeding vaporized charge material into said are discharge to provide ions, and means for extracting and accelerating said ions from said are chamber; the improvement comprising a current coil mounted within said are chamber, said current coil having elongated upper and lower legs and a cross leg, said upper leg extending parallel to and above said are discharge, said lower leg extending parallel to and below said arc discharge, and said cross leg extending behind said are discharge and communicating between said upper and lower legs, said coil providing a magnetic field upon the passage of electric DC. current therethrough for promoting the migration of the ions formed in said arc discharge through said exit slit, thereby effecting a substantial increase in the operating efficiency of said source at about one half the normal vapor feed rate.

References Cited UNITED STATES PATENTS 3,172,007 3/1965 Hanks et a1 315-14 2,704,335 3/1955 Luce 31363 2,798,181 7/1957 Foster n 3l3--63 X 3,084,281 4/ 1963 Mills 313-231 X JAMES W. LAJWRENCE, Primary Examiner.

PALMER C. DEMEO, Assistant Examiner.

US. Cl. X.R. 

